1. Field of the Invention
The present invention relates to a lens barrel which can be retracted to an accommodation state in which the length of the lens barrel is shorter than that in a ready-to-photograph state when no photographing operation is carried out.
2. Description of the Related Art
Miniaturization of cameras is always advancing, and therefore, miniaturization of retractable photographic lenses for cameras, which retract to reduce the length thereof in a non-operating state, has been in increasing demand. As a solution to meet this demand, the assignee of the present invention has proposed a retractable lens which is disclosed in U.S. Pat. No. 6,978,089 (U.S. patent application Ser. No. 10/368,342). This retractable lens is characterized by having a plurality of optical elements of a photographing optical system aligned with an optical axis in a ready-to-photograph state (photographable state), and apart of the plurality of optical elements is radially retracted to a position (radially-retracted position) deviating from the optical axis of the remaining optical elements while being retracted, together with the remaining optical elements on the optical axis thereof, in the direction of the optical axis of the photographing optical system when the photographic lens is fully retracted. When this retractable lens is in an accommodation state (fully retracted state), a reduction in length of the retractable lens is achieved by an arrangement wherein a radially-retractable optical element, which has been retracted from an optical path on the optical axis, is positioned in an axial range substantially identical to an axial range in the optical axis direction in which the remaining optical elements that remain on the optical axis are positioned.
In the lens barrel including a radially-retractable optical element like the above described radially-retractable optical element, the radially-retractable optical element must be moved to the photographable position thereof on a photographing optical axis securely with a high degree of precision when the lens barrel moves to an operating state (ready-to-photograph state) from a non-operating state. For instance, in the lens barrel disclosed in the U.S. Pat. No. 6,978,089, the radially-retractable optical element holding frame which holds the radially-retractable optical element is biased in a direction toward the photographable position thereof while the retractable lens is provided with a stop mechanism for determining the limit of movement of the radially-retractable optical element holding frame in this biasing direction to carry out positioning of the radially-retractable optical element. In this type of positioning mechanism for the radially-retractable optical element, it is required that the radially-retractable optical element does not either come off or slip out of place at the stop mechanism even if a strong impact is applied thereto and that the radially-retractable optical element is made to stop securely with stability at the photographable position thereof. More specifically, if the movable support mechanism for the radially-retractable optical element holding frame is provided with an amount of play which allows the radially-retractable optical element holding frame to move slightly in an optical axis direction (thrust direction), there is a possibility that the engagement of the radially-retractable optical element holding frame with the stop mechanism accidentally releases in the event of the stop mechanism receiving an external impactive force when, e.g., the camera in an operating state is accidentally dropped on the ground. To prevent this problem from occurring, there is a demand for a support mechanism which prevents the radially-retractable optical element holding frame from moving in the thrust direction unnecessarily and makes it possible to stop and hold the radially-retractable optical element securely at the photographable position thereof.